1. Field of the Invention
This invention relates to improvements in circuits and methods for digital servo signal demodulation in mass data storage devices, or the like, and more particularly to improvements in such circuits and methods using weighted peak sample averaging techniques.
2. Relevant Background
In modern computers and computer-type applications, one or more mass data storage devices may be employed. Typical mass data storage devices, often referred to as hard disk drives, CDROMs, or the like, have one or more rotating data storage disks. The data storage disks may have thereon, for example, a spinning magnetic, optical, or other media that can contain data. In such devices, data is generally recorded in certain field portions of rings or tracks that are physically located progressively radially outwardly from the center of the disk.
Preceding each data packet, usually the manufacturer of the mass data storage device records a servo section that contains, among other things, a number of servo bursts or pulses in each predefined servo section. The servo pulses enable various functions to be performed, including the alignment of the head or data transducer to the center of the data track, and the aiding of synchronizing the data decoding with the timing of the data recorded on the track, and so on.
Typically, four or six servo bursts are provided, with each burst being laterally offset by predetermined amounts from the centerline of the track with which it is associated. The bursts are written in quadrature in adjacent tracks, so that if the track is being properly followed by the head or data transducer, two bursts of equal amplitude are detected. Otherwise, the bursts will not appear of equal amplitude, and information sufficient to enable proper lateral head alignment with respect to the track can be decoded. For example, if one burst is at maximum amplitude, and the other is zero, the head is skewed to one side of the track and needs to be realigned. Thus, it is important that the burst amplitude be accurately detected in order to be able to derive proper positioning information. This process is referred to as xe2x80x9cservo demodulationxe2x80x9d.
In the past, servo demodulation has been done in the analog domain by analog circuitry in the read channel of the mass data storage device. This has been done using a number of analog peak detectors, which have to be accurate and have to be able to respond quickly to amplitude changes, that is, have to be of high speed. Moreover, the offsets between adjacent peak detectors (i.e., peak detectors that detect the amplitudes of adjacent servo bursts) have to be well controlled. Typically, for example, if four servo bursts are required to be detected, four separate analog peak detectors are needed.
In operation, differences between adjacent servo bursts are developed. For example, a difference between burst A and burst B is generated, and if a voltage offset is present between the detector circuits, the offset contaminates the development of the difference. Consequently, critical circuit matching techniques are required to minimize the offset signal contamination.
Typically, each of the servo bursts to be detected includes a number of dibit pulses similar in waveshape to sine waves. The number of pulses is fixed depending upon the format selected by the manufacturer and generally is on the order of 4 to 10 in each servo burst. The peak values of the dibit pulses are generally detected using a capacitor that is charged by the dibit signal. In order to eliminate the possibility of detecting noise, some means is generally provided to control the maximum rate that the detecting capacitor can charge. As a result, several dibit pulses need to be processed before a peak can be detected and declared. Moreover, the analog value that is developed on the capacitor can only be held for a finite time, before it begins to decay. This can be disadvantageous.
As integrated circuit processes are becoming more and more reliant on CMOS devices, and more particularly to digital CMOS devices, bipolar transistors are becoming less available. As a consequence, it is becoming more difficult to design analog circuits in applications in which they formerly were readily available. Even if analog devices were to be provided in emerging digital CMOS processes, they currently do not perform very well.
What is needed, therefore, is a peak detector design and method that can be implemented in the digital domain to take advantage of the available digital CMOS processes. In addition, what is needed is the provision of a way to filter out noise during digital peak detection. In addition, what is needed is the provision of a way to hold the detected peak value for at least a time sufficient to perform the necessary digital processing using the detected peak value.
A servo signal is demodulated using a digital peak detector to minimize the effects of signal noise and system disturbances. The peak samples are weighted and averaged according to a novel algorithm.
One of the advantages of the circuit and method presented is the ability to filter out noise that may occur during digital peak detection.
Thus, in accordance with a broad aspect of the invention, a method is presented for demodulating servo bursts received from a rotating data medium. The method includes receiving a sampled analog data signal and converting the analog data signal into digital data words. Thus at least a plurality of digital data words represent individual cycles of a servo burst. The method also includes performing a full-wave rectification of the digital data words to represent both positive and negative burst values and determining an average of the digital data words for each burst.
According to another broad aspect of the invention, a method is presented for performing demodulation of servo bursts pre-recorded in quadrature along laterally offset locations from a centerline of a track of a rotating data medium. The method includes reading analog signals along the centerline representing the servo bursts on each side of the centerline. An analog-to-digital conversion of the analog signals is performed at predetermined sample intervals to produce digital words indicative of instantaneous magnitudes of the servo bursts. Digital peaks are determined of the digital words of the analog signals on opposite sides of the centerline from values at the predetermined sample intervals. Adjacent ones of the determined digital peaks are subtracted to determine an alignment of a head along the centerline of the track.
According to yet another broad aspect of the invention, a circuit is presented for demodulating servo bursts detected from a data medium. The circuit includes an A/D converter to receive the detected servo bursts to convert the servo bursts into digital data words at predefined sample times. A peak detector determines respective peaks of the digital data words. A circuit discriminates the digital data words to determine the largest and the smallest peak values so that they can be discarded if desired by the user. A circuit weights the peaks of the digital data words with predefined weights, and accumulates the weighted peaks. A circuit determines a sum of the weights applied to the digital data words, and a circuit divides the accumulated weighted peaks by the sum of the weights.